This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for advancing incremental portions of a photoconductive belt employed therein.
In a typical electrophotographic printing machine, the photoconductive member is charged to a substantially uniform level. A light image of an original document irradiates the charged portion of the photoconductive member selectively dissipating the charger thereon. This records an electrostatic latent image of the original document on the photoconductive member. The electrostatic latent image is developed with charged particles. These particles are transferred from the latent image to the sheet of support material. Thereafter, the particles are permanently affixed to the sheet of support material forming a copy of the original document.
In general, the photoconductive member is charged each time a copy is made. After a plurality of copies is have been made, i.e. 10,000 or more copies, the photoconductive layer frequency suffers fatigue from discharge breakdown. When the photoconductive material has fatigure, it shows a markedly lower efficiency in forming electrostatic latent images and in transferring the tone powder image to the sheet of support material. At this time, it becomes extremely difficult to produce high quality copies. Thus, the photoconductive member should be replaced. Frequently, it is difficult to change the photoconductive member. Thus, various techniques have been developed to introduce an unused photoconductive member into the operative location of the electrophotographic printing machine. For example, U.S. Pat. No. 3,877,806 issued to Schrempp et al in 1975 discloses a photoconductive web stored on a spool. The belt is incrementally advanced from the spool land entrained about a pair of opposed spaced rollers to form a triangular belt configuration. An alternate approach is described in U.S. Pat. No. 3,926,515 issued to Nagahara in 1975. This patent teaches the use of a photoconductive strip wound on a supply reel and a take-up reel. Both the supply reel and the take-up reel are disposed within a cylindrical support. A photoconductive strip is advanced, in discrete steps, so that the entire portion of the photoconductive strip entrained about the cylindrical member is removed therefrom when it is fatigued. U.S. Pat. No. 3,600,086 issued to Cates in 1971 discloses an apparatus for automatically advancing or replacing a reusable photoconductor element in an electrophotographic printing machine. The photoconductive element is stored on supply and take-up rolls located within the interior of a drum. A counter is actuated each time a copy is reproduced. When a pre-set number of copies have been made, the electrophotographic printing machine is automatically cycled into a photoconductor advance mode. This causes a new length of photoconductive material to be drawn from the supply roller and disposed about the outer periphery of the drum. A second counter records the number of time the photoconductive material is advanced and provides an indication to the machine operator when the photoconductor supply is exhausted. U.S. Pat. No. 3,588,242 issued to Burlier in 1971 discloses an electrophotographic printing machine having a drum which permits automatic advancement of a reusable photoconductive web. The photoconductive element is stored on a supply roll and advanced to a take-up roll. Both of the rolls are located within the interior of the drum. Advancement of the photoconductive element is initiated by engaging a clutch which drivingly couples a normally free-wheeling drive train to the advancing mechanism. This causes advancement of the photoconductive element as the copy drum is rotated by the drive motor used to turn during the copying operations. A metering apparatus is located within the interior of the copy drum and actuates a switch to terminate the advancing operation when a pre-determined length has been advanced.
Although the photoconductive drum structures hereinbefore described effectively provide a long life by virture of the storage of replacement sections of the photoconductive belt therein, these mechanisms are complex and frequently difficult to maintain.
It is an object of the present invention to improve the photoconductive belt incrementing mechanism employed in an electrophotographic printing machine.